In most cases, partial discharge phenomena are due to insulation defects in the distribution elements forming part of the electric power distribution system, the distribution elements consisting of, for example, cables, transformers, switches, electrical connections, etc.
Partial discharges have damaging effects on the medium in which they occur. In a solid or liquid medium, they cause a slow but continuous degradation, ending with the dielectric breakdown of the insulating medium. In a gaseous medium, such as for example, air, partial discharges cause the known corona effect, which comprises consequences directly perceivable by sense of sight, hearing or smell. However, there are other consequences that are not detectable in a simple manner, such as heat generation, power losses, mechanical erosion of ionically bombarded surfaces, interferences with radio waves, etc.
Partial discharges can have very serious consequences if they occur and go unnoticed. If the problem remains unsolved, deterioration will occur until the distribution element is completely destroyed. Replacing or repairing the damaged distribution element can be very costly and can involve a power cut in the distribution system for a long period of time, as well as significant economic losses for electric utilities. The key for preventing any possible problem is to detect and indicate partial discharges. An early detection and, accordingly, indication of partial discharges can aid in preventing risks and performing suitable installation maintenance.
Ultimately, it is important to inspect the presence or absence of partial discharges and prevent faults in the distribution elements, such as for example, in cables, as well as prevent economic losses for electric utilities, service cuts to consumers involving long periods until the system is re-established, etc.
Physical systems comprising sensors for capturing signals to be measured, devices for recording the signals, means for transmitting the signals, devices for storing information, means for processing the results, etc., are used to carry out an evaluation of the state of insulation. In this sense, there are monitoring systems which are used to perform periodic or continuous evaluations of the electric power distribution system and of the distribution elements forming part of the system. However, on the other hand, there are no systems or devices which allow detecting and indicating partial discharges and which are integrated in the corresponding electrical equipment forming part of the installations (such as for example, in an electric transformation substation), and which are continuously indicating the presence or absence of partial discharges verifying the presence or absence of the partial discharges in a simple manner, such as for example, visually and/or audibly. Installations with this type of mentioned systems which allow early detection and accordingly indicating/visualizing the existence of partial discharges in a simple manner without having to use other devices, systems, etc., external to the installation are not known, which can lead to there still being partial discharges that are not detected in time, and to the undetected partial discharges causing adverse effects such as those mentioned above.
Patent document CN203773010U which mentions a solution relating to a partial discharge monitoring instrument in electric cubicles, which comprises a central processing unit, a partial discharge signal processing circuit, a partial discharge indicating circuit, etc., can be mentioned as an example. This solution relates to a system or instrument which is used for performing a continuous or periodic evaluation of the state of insulation or of the system, which involves functions such as measuring partial discharges, locating the position of the discharges in the system, identifying the partial discharges, recording or storing data, communications (alarms, state of insulation, etc.), control functions, etc., in addition to indicating the presence of partial discharges. Therefore, it does not relate to a system for detecting and indicating partial discharges which allows a quick and simple verification of the presence or absence of the discharges, such as for example, the verification that could be performed by an operator by simply entering an installation such as an electric transformation substation, but rather relates to a more complex and expensive system which is used for evaluating the system or the state of insulation once partial discharges are detected.
On the other hand, capturing voltage signals through screens incorporated in the bushings of the electrical equipment, such as for example, electric cubicles, transformers, etc., is known. These captured voltage signals allow carrying out applications, such as for example, detecting, measuring and indicating voltage, sometimes using more than one screen for capturing the voltage signals, i.e., one screen for each of the applications. In this sense, patent EP0851442B1 is known, which describes a bushing incorporating two screens, one of them capturing a voltage signal for voltage detection application and the other capturing a voltage signal for voltage measurement, so it is based on the use of two different voltage signals one for each of the applications, this significantly increasing its complexity and associated costs.
Furthermore, referring to non-patent literature, it is known the article of J. P. Steiner: “Partial Discharge—Part IV: Commercial PD testing” (1991, IEEE), which is concerned with commercial applications of partial discharge testing.